|By Hilary Russ

|By Hilary Russ

|By Hilary Russ

|By Hilary Russ

|By Hilary Russ

|By Hilary Russ

|By Hilary Russ

NEW YORK (Reuters) - The U.S. federal government on Friday marked its return to the rebuilt 1 World Trade Center, moving its New York City offices back to Lower Manhattan 15 years after the Sept. 11 attacks that had reduced the site to rubble.

Also known as the Freedom Tower, the 104-story 1 World Trade Center is the tallest skyscraper in the Western Hemisphere, at 1,776 feet (541 meters).

Construction began in 2006 and the building opened in 2014 when media company Conde Nast, the anchor tenant, moved in. About 67 percent of its 3 million square feet is now leased.

The federal government was one of the first tenants in the original World Trade Center in the 1970s, said Port Authority of New York and New Jersey Executive Director Patrick Foye. The General Services Administration had leased space at 6 World Trade Center before it was destroyed in the attacks.

The government became the third tenant in the new building when the General Services Administration signed the lease on its behalf in 2012.

On Sept. 11, 2001, four U.S. commercial airplanes were hijacked and crashed into the World Trade Center's twin towers, as well as the Pentagon building near Washington D.C. and a field in Pennsylvania, killing nearly 3,000 people.

The federal government's return to the World Trade Center sends a "message to the entire world that we will never, ever renounce our values or be afraid," New York City Mayor Bill de Blasio said.

'AMERICANS ROSE UNITED'

More than 1,000 employees of the GSA, the Federal Emergency Management Agency, and U.S. Customs and Border Patrol had moved into the space by March, a spokeswoman said. The lease for the approximately 220,000 square feet is $15 million per year.

Still, not everyone was happy about the return of government agencies to the building. In 2015, six GSA employees sued to try to block the move, saying they feared the rebuilt tower would again be a target for possible attacks. A federal judge in Manhattan threw out the case in June.

In Washington on Friday, members of the U.S. House of Representatives gathered on the exterior steps to the chamber for a remembrance ceremony and sang God Bless America.

Recalling "that terrible day," House Speaker Paul Ryan, a Republican, spoke of the first responders "who went rushing into danger when the whole world was running away from it."

House Minority Leader Nancy Pelosi, a Democrat, told the assembly that because of the first responders' heroic efforts, "Americans rose united" from the rubble of the attacks.

For one of those first responders, Michael Byrne, a former New York City firefighter who is now a senior FEMA official, the return of federal government employees to the World Trade Center site is deeply personal.

At the event in Lower Manhattan, Byrne said that as he walks past the memorial to his office each morning, he bids "hello" to friends who died in the 2001 attacks and asks for their blessing.

"We feel the renewed commitment in this beautiful building to continuing the mission for which our former friends gave their life," he said.